1. Field of the Invention
The present invention relates to an ion implantation apparatus and a method of cleaning an ion implantation apparatus.
2. Description of the Related Art
One of the standard practices in semiconductor manufacturing is to implant ions into a semiconductor wafer for the purpose of modifying conductivity or modifying the crystal structure of the semiconductor wafer. An apparatus used in this step is generally called an ion implantation apparatus.
For example, a fluorine compound gas is used as a gas provided to an ion source in these ion implantation apparatuses. By inducing plasma discharge in the source gas or irradiating the gas with an electron beam, atoms included in the source gas are ionized. Ionized atoms are used for ion implantation. Some of the atoms are deposited inside the apparatus as a fluorine compound.
An ion implantation apparatus needs to be maintained periodically to exchange components or clean the apparatus. If the apparatus is opened to atmosphere while the fluorine compound remains deposited inside a vacuum chamber containing an ion source in the apparatus, the moisture in the incoming atmosphere and the fluorine compound react with each other. The reaction produces a corrosive hydrogen fluoride gas, which makes the maintenance work difficult.
For safety reason, therefore, it is preferable to reduce the amount of deposited fluorine compound to a certain degree before opening the apparatus to atmosphere. More specifically, a method is devised to introduce atmosphere containing moisture into the vacuum chamber of the apparatus, cause the deposited fluorine compound to react with the moisture, and evacuate the chamber via an abatement system until the concentration of hydrogen fluoride (HF) produced drops to a permitted exposure limit or below.
However, the related-art method introduces atmosphere into the apparatus by taking advantage of a pressure difference between the atmospheric pressure and the pressure inside the apparatus so that the atmosphere entering the chamber is decreased in association with a decrease in the pressure difference. As a result, the generation speed of hydrogen fluoride is decreased gradually so that it takes time to decompose and remove the deposited fluorine compound. Since the amount of atmosphere that can be introduced at a time is limited, it is necessary to open and close a valve repeatedly so as to introduce atmosphere into the apparatus and evacuate the apparatus alternately. For this reason, it takes a long time to remove the deposited fluorine compound, and so there is room for further improvement in respect of reduction of maintenance time.